Electronic devices, of the type such as transistors, are being packaged for operation in apparatus, such as computers, in progressively greater density. Even though the individual electronic device is physically small and the power dissipated therein is also small, the large numbers in a small area together with the general temperature sensitivity of electronic devices operate to require closer temperature control. Where the electronic device is operated at superconductive temperatures, there is also a need for close temperature range control at a very low temperature level, since superconductive devices must be operated at low temperatures.
There are also performance advantages to operating particular types of semiconductor circuits at very low temperatures. Of these types the CMOS and GaAs device based circuits are well known. A discussion of many of the considerations involved and the advantages of low temperature operation appear in the article "A Cryogenically Cooled CMOS VLSI Supercomputer" in the journal "VLSI Systems Design", June 1987, pages 80 to 88.
Open cycle type cooling systems are generally, both in economy and efficiency, unsuitable for the higher packing density of electronic devices and particularly in conditions where superconductive or cryogenic temperatures are involved.
The closed cycle type cooling systems thus far in the art generally have a refrigerator thermally coupled to a cryogenic fluid in which the electronic devices are positioned. A portion of the refrigerator and the electronic device assembly is contained in a vacuum sealed container.
One example of a closed cycle type cooling system is described in IBM Technical Disclosure Bulletin 18, 4 Sep. 1975, pages 1226-1229, employing liquid nitrogen as a heat transport fluid in which the electronic devices are immersed, the fluid transports the heat by boiling and condensation and the refrigerator is mounted outside and thermally coupled into a flask that houses the fluid and the electronic devices.
Another example of a closed cycle type cooling system is described in U.S. Pat. No. 4,223,540 in which a multistage refrigerator is positioned in one port of a thermal flask containing the refrigeration fluid and the electronic devices are immersed in the refrigeration fluid by positioning them through another port in the flask.
In the progress of the art, many reasons are being encountered for being able to remove the electronic devices. The reasons run from merely the repair or replacement of an individual device or integrated circuit of devices through entire repopulation of devices as more advanced capability is built into more densely packed and intricately wired assemblies. At the present state of the art in the closed cycle type of cooling systems, it is necessary to engage in a major disassembly in order to get to the electronic devices.